Expandable aqueous foams are known and have been used for various purposes such as fire fighting foams, and the like. In U.S. Pat. No. 4,541,947, assigned to the same assignee, the use of high expansion foams for crowd control and other uses is described. In U.S. Pat. Application Ser. No. 744,511, filed June 13, 1985, now U.S Pat. No. 4,589,341, granted on May 20,1986 and assigned to the same assignee, the use of high expansion foams for blast control and suppression of blast effects is disclosed. In U.S. Pat. Application Ser. No. 777,921, filed Sept. 19, 1985, refiled on Mar. 27, 1987 as continuation application Ser. No. 030,893 (now abandoned) and assigned to the same assignee, the use of such foams as system to encapsulate toxic and other materials is disclosed. In U.S. Pat. Application Ser. No. 781,248, filed Sept. 27, 1985, (now abandoned) and assigned to the same assignee, the use of such foams as a security system is described.
It is apparent from the above that stable high expansion aqueous foams have special utility in fields well known to date. In U.S. Pat. No. 4,442,018 of Apr. 10, 1984 issued to Peter B. Rand, a high expansion, stable aqueous foam is described which includes a water soluble polymer of the polyacrylic acid type having a molecular weight of about 500,000, a foam stabilizer of dodecyl alcohol, a surfactant, and a solvent, all in water is used as a foam concentrate for use in producing what is said to be an improved stabilized high expansion foam.
U.S. Pat. No. 4,439,329 of March 27, 1984 and issued to Kliner et al also discloses a fire fighting foam which is said to be stable through the use of a oleophilic hydrocarbamyl sulfide terminated oligomer as the surfactant.
The generating equipment for producing such expandable foams is well known and is described in the patents and applications previously identified.
The stability of foams is generally identified in terms of the liquid drainage rate of the foam. In effect this is a measure of the rate at which the liquid water drains from the foam and reflects the density stability of the foam and is a standard frequently used. Typically it is referenced in terms of a percentage by weight for a period of time, e.g., 50% by weight drainage for 30 minutes.
One of the important qualities of a foam concentrate is the storage ability of the foam and the ability of the concentrate to remain properly dispersed during shipment and storage. If there is separation of the component of what is usually a multicomponent mixture, the concentrate may have to be remixed before use. This, of course, presents significant problems at the site of use since it is usually a situation where there is no immediately available mixing equipment and the separated components may not be easily redispersed merely by shaking the concentrate. Even if the materials may be redispersed, this may take time in a circumstance in which time is critical, for example, at the site of a dangerous fire, toxic spill or immediate security problem, see the patents and applications to which reference has already been made.
Another aspect of such foams is the impact which the same may have on the environment. Materials which are not biodegradable may obviously present serious consequences in use and thus might be used only as a last alternative due to environmental problems. This consideration may severly restrict the use of expandable foams where their use is clearly appropriate as the most effective solution to an immediate and perhaps emergency problem. For example, the alcohols used in the foam of the Rand patent tends to reduce the biocompatibility of the foam and foam concentrate there disclosed.
Experience with the Rand type of foam has also brought up some added problems, although that foam and concentrate are said to represent an improvement in terms of stability. More specifically, it is believed that foam stability improvement is achieved in that foam material is reinforced by a polymer which is non-reactive in the sense that the polymer is dispersed and physically rather than chemically associates with the small bubbles of the foam to inhibit water drainage and thus bubble collapse. A physical association in the foam operates for a limited period of time and as the water is freed from the foam, the foam density is reduced as measured by the drainage rate, i.e., the rate at which water liquid is released with the result that the bubbles collapse. In a sense the polymer is a fiber type of element that tends to hold the bubbles together, but the polymer may be relatively insoluble in water and thus the alcohol is used as a cosolvent.
It has also been noted that some of the components of the Rand foam tend to gel when exposed to humidity during manufacture, that is, the polymer and the alcohol cosolvent must be anhydrous or the components tend to form a gel which is difficult to redisperse during mixing of the components. The attempted manufacture of commercial quantities of this prior art foam concentrate from materials as commercially available, i.e., in a non-anhydrous form has indicated that the addition of the polymer tends to produce a concentrate which is non-uniform in composition, i.e., one or more of the components tend to separate out. There have also been mixing and subsequent handling problems and separation. The biocompatibility problem has already been discussed. All in all, the Rand type foam is difficult and expensive to manufacture.
More specifically, the procedure for making the Rand product involves the use of polyacrylic acid said to be used to viscosify aqueous systems in the cosmetics field. The polyacrylic acid polymer is usually dissolved in an alcohol of C2 to C5 in length. These alcohols, especially the C3 and above alcohols are difficult to use if they have absorbed moisture and if the polymer has absorbed moisture. When the polymer is mixed with the alcohol, the result is a gummy mass which is difficult, if not impossible to use. While the polymer may be dried overnight in an oven at 65 degrees C., this is not a practical commercial operation especially if the alcohol also has to be treated, as by flow through a molecular sieve to form an anhydrous alcohol. These materials are also hygroscopic and tend to pick up moisture from the air, also leading to manufacturing problems. It is significant that the Rand concentrate also has a viscosity of about 50 centipoises.
At this relatively high viscosity it is difficult to form a thoroughly mixed prefoam mixture, i.e., the water diluted mixture from which the foam is formed. Normally the prefoam mixture is a dynamic mixing operation in which the concentrate is mixed with water at the generator and then flowed to the bubble forming mechanism, normally some form of screen. With uneven mixing of the prefoam material, there are concentrate rich and concentrate starved sections which tend to produce foams of less than the desired quality and uniformity. While this could be overcome by thoroughly premixing the concentrate to form the prefoam mixture, that is undesirable and not effectively achieved at the site of use.
The above difficulties have severely limited the use of the Rand foam and have effectively prohibited its use in areas other than those mentioned.
More specifically, expandable aqueous foams which are stable and biodegradable offer significant potential as a delivery mechanism for various products such as insecticides, pesticides and the like and other agricultural treatment products. By incorporating such products in a stable expandable foam they may be delivered precisely and in a controlled and defined manner to the site of application without concern that such products will be dissipated over a wide area by the wind. Since the foam includes a surfactant, the plants are wetted easily and the effective ingredient is effectively placed over the entire foliage. This type of delivery system is particularly effective for herbicides where it is desired to control accurately the site of delivery and the application. In effect the foam bun remains in place for some period of time and the effective delivery system tends to reduce the amount of such materials which need to be used since the application is controlled by control of placement of the foam bun. A stable, expandable foam in accordance with the present invention may also be used in certain types of agricultural applications to protect against crop freezing.
Another use of the foam of this invention is as a litter for laboratory and test animals. The practice to date has been to use newspaper or some form of dry litter. The objection is the odor generated by the animal droppings and the difficulty in cage and pen clean-up as well as the general sanitary condition of the cages and animals. The use of a foam of the type here described, which is stable and biodegradable offers several advantages. First, the surfactant, which acts as a detergent, tends to keep the pens and cages clean and is easily rinsed away along with all of the animal waste. Odors are suppressed since the foam remains as a blanket in the cages and prevents or at least inhibits migration of the odor. Further, the general cost is less due to the manual operations involved in prior litter systems.
It is thus an object of the present invention to provide an improved foam concentrate and foam system which is easier to manufacture and which is relatively stable in comparison to prior art foams.
It will be apparent from the detailed description which follows that there are several advantages to the present invention which will become apparent to those skilled in the art.